grating is used with the FUV-MAMA
and provides echelle spectra at a resolving power of 45,800 from ~ 1144–1710 Å.
A single E140M
echellogram covers ~600 Å, however at wavelengths longward of 1649 Å, the echelle orders overrun the width of the detector in the dispersion direction, so there will be three small gaps in the wavelength coverage. One gap of ~0.2 Å, one of ~0.4 Å, and one of ~0.7 Å occur between 1649 and 1700 Å.
The separation between orders is ~15 pixels
(or 0.44 arcseconds) at 1150 Å and ~33 (0.96 arcseconds) at 1700 Å.
Also note that while the spectral format of
the E140M extends down to 1123 Å, when combined with the HST primary and secondary, the total system throughput for external targets becomes extremely small below about 1144 Å.
Point source sensitivity assumes full transmission (zero slit losses). Diffuse source
sensitivity assumes a 0.1” wide slit. To convert point source sensitivities to diffuse source sensitivities multiply the point source values by the grating spatial (cross dispersion) plate scale in units of arcseconds per pixel and by the width of the desired slit in units of arcseconds.
The top axis displays constant Fλ
values corresponding to the STMAG units (V+STMAGλ
) on the bottom axis. Recall that STMAG=0 is equivalent to Fλ
= 3.63E-9 erg/cm2
/s/Å. The curves are labeled with exposure times in seconds.